The invention relates to a method of fluid ejection under controlled parameters, such as flow rate, pressure and volume, in a device intended to infuse fluids to patients, like those for intravenous, parenteral, enteral, antibiotics and other medical uses, as well as simply pumping fluids contained in flexible plastic bags.
Infusion fluids for medical use are generally supplied from flexible plastic containers attached to infusion tubings. The most common method is by passive, gravity-feed infusion, accomplished by suspending the bag from a pole, at a certain height relative to the patient. Sufficient pressure is created by gravity acting upon the fluid in the reservoir, with the flow rate being controlled by a manually operated valve. For these suspended bags, a flexible encasement with a chamber may be provided. Air is filled in the chamber at a given pressure, to increase the flow rate from the bag, with the pressure in the encasement being controlled by a manometer.
As an alternative to those gravity-feeding, low and unprecisely controlled flow rate devices, mechanically driven devices have been developed. The potential advantage of these mechanically induced pressure devices is the possibility to more precisely control the fluid ejection parameters, achieving at the same time, higher flow rates of fluids contained in flexible plastic containers for a wide range of applications. For example, Fletcher et al. U.S. Pat. No. 4,033,479 discloses an infusion device by mechanically pressing a fluid-containing reservoir at a constant pressure. Cherkin U.S. Pat. No. 2,761,445 describes a device containing a bag pressing platform moved by a variable speed motor. Another example of flow controlled infusion devices for squeezing a flexible bag is described by Campbell, U.S. Pat. No. 5,232,439 and U.S. Pat. No. 5,423,759, which describes an infusion pump and a valve system for its control. The infusion tubing is mechanically closed depending on the pressure of the fluid in the bag measured by a sensor pressed against the outside of the reservoir by a presser plate.
It is an object of the present invention to provide a simple and precise method to eject and control the fluid discharge parameters, eg., volume, flow rate and the pressure needed to achieve it. The invention includes a precision potentiometer attached to a motor driven shaft with a worm gear. The precision potentiometer continuously detects shaft rotation speed. This value is compared to the calculated parameters in a central processing unit (CPU), taking into account the operator entered required parameters by means of input buttons. The required parameters may be visualized in a liquid-crystal display. This computer assisted, precision potentiometer controlled, fluid-contained flexible bag squeezing device, is potentially simpler and more precise than previous devices, due to its capability to better control the squeezing pressure on the bag. The precision potentiometer controls the motor-driven shaft rotation speed. The CPU can precisely control the electric current to the motor, thereby controlling motor speed and torque, with assistance of a microprocessor-based circuit and appropriate software. The desired flow rate may thereby be achieved.
Other and additional objects are apparent from the following discussion of the invention and its preferred embodiment.